Production of urea



Patented July 19, 1932 UNITED STATES ERNST xnss AND MAX GUENTHEB, or MANNHEIM, enmvmnins srenons ro I. G. FARBENINDUSTRIE AKTIENGESELLSCHAIT, or rRANxFonT-oN-TnE-Mun, .ena-

MANY

rnonucrron uitfizl No Drawing. Application filed February 28,1930, siiai No: 455,556; gii'idin assassin "2.1155131" The present invention relates to the production of urea.

It is already known that urea can be prepared from carbon dioxide and ammonia at elevated pressures and at elevated temperatures. Industrially this process is usually carried out in two stages by preparing ammonium carbamate as an intermediate material, and then obtaining urea therefrom by heating. In this manner, however, only a part of the carbon dioxide employed is converted into urea.

We have now found that the carbon dioxide introduced into this process may be practically completely converted into urea in one operation by employing mixtures of ammonia and carbon dioxide, which contain an amount of ammonia, which is at least 4 times, and preferably still more times, the amount so stoichiometrically necessary according to the equation:

CO2 :NH NH H O.

In order to obtain as high a velocity of conversion as possible, the temperature should advantageously be higher than 150 (1, but as a rule not higher than about 200 C. It is also essential for the success of the process according to this invent-ion that elevated pressures above the critical pressure of ammonia be employed. It is preferable to work at pressures of 4,00 atmospheres and more. In carrying out the process according to the present invention, it must be borne in mind that the yield of urea, calculated on the amount of carbon dioxide used, depends not only on the excess of ammonia, but also on the pressure and the temperature. Thus, when working at 160 C. and 400 atmospheres pressure, the following results are obtained Per cent Theoretical amount of ammonia yield 42.5

At a pressure of 700 atmospheres, a yield of 98 per cent is obtained with an excess of ammonia of cooper cent. Whenwerking' at; given pressure and an excess of ammonia of 700 per cent, a; yield ofonly'37 per cent is'o'btlained at 140 0.; but 91 per bent at 190? G-;- At above 200 (1.,- ;the yieldfdecrasge's again; The process according" to this inver'i tion is a great advance in contrast wane processes already known because the'c'arbw matestage is passed through s'orapidly that pure ureais obtained almost immediately." 1 Catalysts suitable for promoting thereai'c' tion may also be employed; As ,is well known; such catalysts are for example active carbon, alumina, kaolin, silica", firajit self, salts or oxides of the light meta1s',oraeid; Moreover, subordinate. quantities of water may be added-with advantage." I The" process is preferably carried 0* a: cycle returning the excess of ammonia, te se n f he e, a d we, ai advantageously without previously Ireleas ing the pressure, into the reaction chamber y me ns Pf. i w t 'o P mp T ipsei ia: ratio i of theurea and wate may befrec'cd in various ways, preferablyby cooling. y a Or on-Se, materials which re not ked b th P i an nlfi e readi d, should be employed for the construction; of g6 the pressure vessels and conduits It is pref erable to work in apparatus, which, are-constructed of or lined with" cast iron, or copper or lead or nickel or their alloys, as for example the alloy known under the registered trade mark of Monel metal, or bronze. I

The following examples will further illus- Irate the nature of this invention, but the invention is not restricted to these examples.

, Emample 1 C. and at a pressure eight tion 7 CO2 "i' H2O.

In this manner purevurea is obtained practically immediately. The yield amounts to times the amount required by the equaper cent of the theoretical yield calculated on the carbon dioxide employed.

. I Example 2 Ammoniais continuously circulated at a.

' pressure of 400 atmospheres in an apparatus Carbon provided with circulation means. dioxide is continuously forced into the .reaction"chamber', which is heatedto 160 C. in an amount which is only one tenth of: the amount required by the equation in Example 1- calculatedfwithreference to the ammonia present in thejreaction chamber.. The urea formed is separated together with the water formedduring-the reactionin a cooled vessel, withdrawn and freed from water by evaporation, 7

What We claim is: 7 I

The process of producingurea, which comprises acting with carbon dioxide on ammonia, the latter being at least 4 times in excess over the amount stoichiometrically required, at a temperature of at least above the critical pressure of ammonia.

; 2.} The process of producing urea, which comprises acting with carbon dioxide on ammonia, the latter being at least 8 times in excess over the amount stoichiometrically required, at a temperature ofat least 150 C. and at a pressure above the critical pressure of ammonia. I

'3. The process of producing urea, which comprises acting with carbon dioxide on ammonia, the latter being at least 8' times in excess overthe amount stoichiometrically quired, at a temperature ofat least 150. C. and at a pressure of at least about 400 atmospheres.

" In testimony whereof we set our hands. I

' ERNST KUSS.

MAX GUENTHER.

have hereunto 

